In recent years, attention has been drawn to power feeding systems that perform wireless power feeding (also referred to as wireless power transfer, contact free, or non-contact power feeding) to, for example a portable phone, a portable music player, and other CE (consumer electronics) devices. In such a power feeding system, for example, placing the portable phone (a power receiving device) on a power feeding tray (a power feeding device) allows for charging of the portable phone. Examples of methods of performing such wireless power feeding may include an electromagnetic induction method, a magnetic field resonance method (also referred to as a magnetic resonance method) using a resonance phenomenon, and a magnetic field coupling method.
In the power feeding system, in power feeding, presence of a foreign matter such as a metal piece between, for example, the power feeding device and the power receiving device may lead to possibility of heat generation and lowered safety. Accordingly, there has been a request for detecting the foreign matter and controlling power feeding operation. To detect the foreign matter, various methods have been disclosed. As one example, PTL 1 discloses a power feeding system that detects a foreign matter, in power feeding, on the basis of a difference between feeding power and received power. As another example, PTL 2 discloses a power feeding system that makes detection of a foreign matter before power feeding, and also makes detection of the foreign matter, in the power feeding, in a different way from that of the detection of the foreign matter before the power feeding.